Information Notice 1989-11, Failure of DC Motor-Operated Valves to Develop Rated Torque Because of Improper Cable Sizing
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
February 2, 1989
NRC INFORMATION NOTICE NO. 89-11:
FAILURE OF DC MOTOR-OPERATED VALVES TO
DEVELOP RATED TORQUE BECAUSE OF IMPROPER
CABLE SIZING
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is being provided to alert addressees to potential
,z`problems resulting from motor-operated valves (MOYs) not developing rated
torque because of the failure of the original cable sizing calculations to
include the proper current values and cable resistances.
It is expected
that recipients will review the information for applicability to their faci- lities and consider actions, as appropriate, to avoid similar problems. How- ever, suggestions contained in this information notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
As a part of the Equipment Qualification and Nuclear Plant Aging Studies, the
NRC obtained a motor-operated wedge-gate valve from the Shippingport Atomic
Power Station following its decommissioning.
The valve had been installed
in a secondary system for the 25-year life of the plant. A review of the
maintenance records for the valve and the operator indicated that there were
no reportable incidents associated with either the valve or the operator.
Following removal, the valve and the operator were refurbished by an NRC
contractor and tested to demonstrate the valve's ability to operate at the
conditions expected during the forthcoming testing. The valve, the operator, and the controller were then transported to Germany where they were installed
in the Heissdampfreactor (HOR) decommissioned reactor test facility as part of
a jointly sponsored seismic test research program. With the exception of the
use of equivalent metric-sized cable, the electrical installation of the
operator was identical to that at Shippingport.
Each test of the valve consisted of a closure cycle, an opening cycle, and
a final closure cycle. When the data from these tests was analyzed, it was
determined that the valve had routinely failed to fully seat during the second
closing cycle of each test which had subjected the valve to system pressure and
flow and ambient temperature conditions. In addition, the valve had routinely
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IN 89-11 February 2, 1989 failed to fully seat during both closing cycles of each test which had sub- jected the valve to system pressure, flow, and elevated temperature conditions.
Further evaluation of the data indicated that (1) although the motor had
stalled, the output torque had not been sufficient to open the torque switch;
(2) the maximum recorded current appeared to be significantly less than that
expected for a stalled motor; and (3) the motor voltage at stall was only
slightly less than the running voltage.
In response to a request from NRC, the
contractor conducted a second series of tests at HDR.
Because of the concern
that degraded voltage might have been a contributor to the failures, the elec- trical instrumentation inputs were moved from the motor control center to the
junction strip in the switch compartment of the motor operator.
The second test series produced the same valve failure pattern that had been
obtained in the initial test series.
As the second test series was thought
to have eliminated degraded voltage as a cause, it appeared that the problem
might be improper motor operator sizing. The NRC requested the contractor to
conduct additional testing to determine whether the motor and the operator had
been properly sized initially or whether they had degraded during their service
at Shippingport. To accomplish this testing, the motor operator and the control- ler were removed from the HDR decommissioned reactor test facility and shipped
to the Limitorque manufacturing facilities for dynamometer testing.
The dynamometer testing of the motor operator by Limitorque demonstrated that
the performance of the motor operator was better than that at HDR, but that the
motor performance was less than that originally specified. It was therefore
decided to perform motor dynamometer testing at the motor manufacturer's
facilities. To accomplish this testing, the motor was removed from the motor
operator and shipped to the motor manufacturer. The motor dynamometer testing
by the motor manufacturer demonstrated that the motor's performance did not
differ appreciably from that of a new motor.
However, before any additional evaluations could be performed, the NRC contrac- tor became aware of the recent MOY failures at Brunswick Steam Electric Plant, Unit 1, which had been described in NRC Information Notice 88-72, "Inadequacies
in the Design of DC Motor-Operated Valves."
Because of the similarity of
conditions noted in the HDR and Brunswick failures, the NRC contractor, working
with Limitorque, focused on the analysis of the cable sizing for the MOY.
This
analysis pointed out the following two factors:
(1) The first factor concerned the current values that should be used to
establish the cable size.
As a motor operator is not a continuous-duty
device, the normal operating voltage and current data contained on the
nameplate are of only limited applicability to cable sizing. Rather, it
is the voltage and current required to develop the rated output torque of
the motor operator that is important.
As the current required for~this
rated torque must be developed during locked rotor conditions, the cable
should be sized on the locked rotor current instead of on the full load
current. The ratio of these currents is quite large as the locked rotor
current is typically in excess of five times the full load current stated
on the nameplate.
IN 89-11 February 2, 1989 (2) The second factor concerned the cable resistance that should be considered
in the analysis.
The wiring diagram for a typical motor operator is shown
in Attachment 1. Significant cable resistances and the location of the
voltage measurement during the second HDR tests are also shown.
Attach- ment 2 presents a simplified schematic of the same circuit. As can be
seen, any attempt to measure the voltage drop at the power supply bus
(i.e., the sum of the voltage drops across the armature and the series
field) includes the resistance contribution from four cables. Even taking
the voltage measurement at the motor (as was done during the second HDR
tests) will result in including the voltage drop across three cables.
From the above information, it can be seen that the required current for the
MOY to develop the design torque should be based on the motor resistance and
the cable resistance (i.e., four times that of a single cable) under a minimum
postulated bus voltage.
As indicated in their August 17, 1988, maintenance update, Limitorque recom- mends that the cable be sized to allow for five times full load current flow at
the minimum voltage condition. This maintenance update also contained a method
for calculating the maximum current draw at locked rotor conditions.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Yun-Seng Huang, NRR
(301) 492-0921 Peter J. Kang, NRR
(301) 492-0812
Richard J. Kiessel, NRR
(301) 492-1154 Attachments:
1. Cable Resistances and Voltage Measurements Identified
2. Motor Functional Schematic
3. List of Recently Issued NRC Information Notices
Cable Resistances and Voltage Measurements Identif ied
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Attachment 3
February 2, 1989 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
89-10
89-09
89-08
89-07
89-06
Undetected Installation
Errors In Main Steam Line
Pipe Tunnel Differential
Temperature-Sensing Elements
at Boiling Water Reactors.
Credit for Control Rods
Without Scram Capability
in the Calculation of the
Shutdown Margin
Pump Damage Caused by
Low-Flow Operation
Failures of Small-Diameter
Tubing in Control Air, Fuel
Oil, and Lube Oil Systems
Which Render Emergency Diesel
Generators Inoperable
Bent Anchor Bolts in
Boiling Water Reactor
Torus Supports
Use of Deadly Force by
Guards Protecting Nuclear
Power Reactors Against
Radiological Sabotage
Potential Problems from
the Use of Space Heaters
Potential Electrical
Equipment Problems
1/27/89
1/26/89
1/26/89
1/25/89
1/24/89
1/19/89
1/17/89
1/11/89
All holders of OLs
All holders of OLs
or CPs for test and
research reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
Mark I steel torus
shells.
89-05
89-04
89-03 All holders
for nuclear
reactors.
of OLs
power
All holders of OLs
or CPs for nuclear
power reactors and
test and research
reactors.
All fuel cycle and
major nuclear materials
licensees.
OL = Operating License
CP = Construction Permit
IN 89-11 February 2, 1989 (2) The second factor concerned the cable resistance that should be considered
in the analysis. The wiring diagram for a typical motor operator is shown
in Attachment 1. Significant cable resistances and the location of the
voltage measurement during the second HDR tests are also shown. Attach- ment 2 presents a simplified schematic of the same circuit.
As can be
seen, any attempt to measure the voltage drop at the power supply bus
(i.e., the sum of the voltage drops across the armature and the series
field) includes the resistance contribution from four cables.
Even taking
the voltage measurement at the motor (as was done during the second HDR
tests) will result in including the voltage drop across three cables.
From the above information, It can be seen that the required current for the
MOV to develop the design torque should be based on the motor resistance and
the cable resistance (i.e., four times that of a single cable) under a minimum
postulated bus voltage.
As indicated in their August 17, 1988, maintenance update, Limitorque recom- mends that the cable be sized to allow for five times.full load current flow at
the minimum voltage condition.
This maintenance update also contained a method
for calculating the maximum current draw at locked rotor conditions.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Yun-Seng Huang, NRR
(301) 492-0921
Peter J. Kang, NRR
(301) 492-0812
Richard J. Kiessel, NRR
(301) 492-1154 Attachments:
1. Cable Resistances and Voltage Measurements Identified
2.
Motor Functional Schematic
3.
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
- C/OGCB:DOEA:NRR*PPMB:ARM
- AD/SAD:DEST:NRR*C/SELB:DEST:NRR
CHBerlinger
TechEd
ACThadani
FRosa
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01/25/89
01/23/89
01/19/89
01/19/89
- DOEA:NRR *EMEB:DEST:NRR *C/EMEB:DEST:NRR*AD/EAD:DEST:NRR*SELB:DEST:NRR
RJKiessel
YSHuang
LBMarsh
JRichardson
PJKang
01/10/89
01/12/89
01/18/89
01/18/89
01/19/89
IN 89-XX
January xx, 1989 (2) The second factor concerned the cable resistance that should be considered
in the analysis. The wiring diagram for a typical motor operator is shown
in Attachment 1. Significant cable resistances and the location of the
voltage measurement during the second HDR tests are also shown. Attach- ment 2 presents a simplified schematic of the same circuit. As can be
seen, any attempt to measure the voltage drop at the power supply bus
(i.e., the sum of the voltage drops across the armature and the series
field) includes the resistance contribution from four cables.
Even taking
the voltage measurement at the motor (as was done during the second HDR
tests) will result in including the voltage drop across three cables.
From the above information, it can be seen that the required current for the
MOV to develop the design torque should be based on the motor resistance and
the cable resistance (i.e., four times that of a single cable) under a minimum
postulated bus voltage.
As indicated in their August 17, 1988, maintenance update, Limitorque recom- mends that the cable be sized to allow for five times full load current flow at
the minimum voltage condition. This maintenance update also contained a method
for calculating the maximum current draw at locked rotor conditions.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Yun-Seng Huang, NRR
(301) 492-0921
Peter J. Kang, NRR
(301) 492-0812
Richard J. Kiessel, NRR
(301) 492-1154 Attachments:
1. Cable Resistances and Voltage Measurements Ideni
2.
Motor Functional Schematic
3.
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCUR
D/DOEA:NRR
C/OG X
RR *PPMB:ARM
- AD/'
CERossi
CHBe
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TechEd
ACThi
01/
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RJKiessel
YSHuang
LBMarsh
JRicI
01/10/89
01/12/89
01/18/89
01/11 tified
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01/19/89 EAD:DEST:NRR*SELB:DEST:NRR
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PJKang
3/89
01/19/89
IN 89-XX
January xx, 1989 (2) The second of these factors concerned the cable resistance which must be
considered in the analysis.
The wiring diagram for a typical motor
operator is shown in Attachment 1. Significant cable resistances and the
location of the voltage measurement during the second HDR tests are also
shown. Attachment 2 presents a simplified schematic of the same circuit.
As can be seen, any attempt to measure the voltage drop at the power
supply buss (i.e., the sum of the voltage drops across the armature and
the series field) includes the resistance contribution from four cables.
Even taking the voltage measurement at the motor (as was done during the
second HDR tests) will result in including the voltage drop across three
cables.
From the above it can be seen that the required current for the MOV to develop
the design torque should be based on the motor resistance and the cable resis- tance (i.e., four times that of a single cable) under a minimum postulated buss
voltage.
As indicated in their August 17, 1988, maintenance update, Limitorque recom- mends that the cable be sized to allow for five times full load current flow at
the minimum voltage condition. This maintenance update also contained a method
for calculating the maximum current draw at locked rotor conditions.
The information herein is being provided as an early notification of a poten- tially significant matter that is under further consideration by the NRC staff.
If NRC evaluation so indicates, further licensee action may be requested.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
Yun-Seng Huang, NRR
(301) 492-0921
Peter J. Kang, NRR
(301) 492-0812
Richard J. Kiessel, NRR
(301) 492-1154 Attachments:
1. Cable Resistances and Voltage Measurements Identified
2.
Motor Functional Schematic
3.
List of Recently Issued NRC Information Notices
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AD/SAIPf EST:NRR
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